The present invention relates to asynchronous transfer mode (xe2x80x9cATMxe2x80x9d) networks, and more particularly to a method and apparatus for detecting and reacting to defects on such a network.
Many modern communications networks are adapted to detect and react to defects that may impair the transmission of data along such networks. Synchronous Optical networks (xe2x80x9cSONETxe2x80x9d), for example, detect network defects and switch the routing of traffic within the network a long differing physical paths in the presence of a defect, to ensure data traffic delivery between end points. Such switching is typically referred to as xe2x80x9cprotection switchingxe2x80x9d.
Modern ATM networks, as for example detailed in International Telecommunication Union Recommendations ITU-T I.326, I.361, I.610, I.630, and I.732, the contents of all of which are hereby incorporated by reference, support similar protection switching in the presence of defects to provide a signal across the network in the presence of signal failure (signal failxe2x80x94xe2x80x9cSFxe2x80x9d), or in the presence of a degraded signal (signal degradexe2x80x94xe2x80x9cSDxe2x80x9d).
As detailed in ITU-T Recommendation I.630, ATM protection switching may be effected for single virtual channels (xe2x80x9cVCxe2x80x9ds); virtual paths (xe2x80x9cVPxe2x80x9ds); and logical groups of VPs or VCs (xe2x80x9cVPGxe2x80x9ds or xe2x80x9cVCGxe2x80x9ds).
SF on an ATM network is often manifested in loss of frames (LOF); loss of signal (LOS); or loss of cell delineation (LCD) at the physical layer carrying ATM traffic. As such ITU-T Recommendation I.630, suggests that a SF may be detected at the physical layer. SD, on the other hand, typically manifests itself in the presence of bit errors within the ATM signal. As such, ITU-T Recommendation I.630 suggests detecting SD within VCs at the ATM layer, by using performance monitoring (xe2x80x9cPMxe2x80x9d) cells. That is, PM cells that may be used to assess the presence of signal degrade are inserted into an ATM stream. Using these inserted PM cells, the quality of user cells may be assessed at a downstream node.
ITU-T Recommendation I.630, however, does not address a mechanism for effecting protection switching for VPs, VPGs or VCGs in the presence of SD. Unfortunately, the use of PM flows for all VCs within a VP, VPG or VCG would require undue network resources, in order to monitor such flows on all VPs within a VPG or all VCs within a VCG.
Accordingly, a method and apparatus that facilitates ATM layer protection switching for VPGs or VCGs in the presence of SD is desirable.
Therefore, in accordance with the present invention, SD is monitored on a subset of VPs within a VPG or within a subset of VCs within a VCG. If SD is detected on this subset of VPs or VCs, all VPs or VCs within the VPG or VCG are switched from a working entity to a protection entity.
In accordance with the present invention, receipt of traffic is switched from a group of working ATM channels/paths to a group of protection ATM channels/paths on a network element in an ATM network. Specifically, ATM monitoring cells are received on a subset of ATM channels/paths of the group of working ATM channels/paths. Each of the ATM monitoring cells includes an error detection code for a plurality of ATM cells received at the network element within an associated ATM channel/path. In response to the error detection codes indicating a degraded signal within an associated ATM channel/path, the network element receives the traffic from all channels within the group of protection ATM channels/paths in favour of receiving the traffic on the group of working ATM channels/paths.
Advantageously then, as SD need only be monitored on a subset of VCs or VPs within a VCG or VPG, network resources are conserved.
Network elements and software may embody these methods.
Other aspects and features of the present invention will become apparent to those of ordinary skill in the art, upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.